1. Field of the Invention
The present invention relates generally to a multi-valve internal combustion engine and more specifically to a valve train arrangement for an internal combustion engine which is arranged to lift two (inlet or exhaust) valves simultaneously.
2. Description of the Prior Art
In a previously proposed arrangement disclosed in Japanese publication "MOTOR FAN" issued on Mar. 1, 1985 by "Saneishobou" Co. Ltd., each cylinder of a twin overhead cam engaine is equipped with two inlet vvalves 1 and two exhaust valves 2. Each pair of valves is arranged to be simultaneously lifted by a single rocker arm 3 which is driven by a single cam.
This arrangement, while reducing the number of major moving parts required to operate the four valves, encounters the drawback that each of the rocker arms 3 is provided with two clearance adjusting screws 4 and associated lock nuts (not illustrated). These clearance adjusting screws 4 and nuts increase the mass of the rocker arms 3. Accordingly, in order to enable high RPM operation, it is necessary to increase the spring constant of the valve springs 5 to ensure that the movement of the valves 1, 2 follows the movement of the cams 6, 7. This increases the friction loss of the valve train and increases the fuel consumption of the engine.
Further, as there is one clearance adjust screw 4 for each valve the number of parts is increased and engine maintenance rendered troublesome as each valve must be individually adjusted.